1. Field of the invention
The invention relates to a process for the manufacture of low molecular monoglycidyl ethers or polyglycidyl ethers of monohydric or polyhydric phenols, having improved properties.
By improved properties there is understood that these glycidyl ethers, obtained by the process:
1. DISPLAY A LOW INTRINSIC COLOUR OF THE GLYCIDYL ETHERS, EXPRESSED BY LOW VALUES OF THE Hazen colour index [ASTM D 1209 / 62, Pt/Co- Standard: Hazen Standard (APHA)] and
2. A LOW CONTENT OF HYDROLYSABLE CHLORINE.
2. Prior art
Processes are known which provide an after-treatment of glycidyl compounds for lightening the colour but which imply an additional process step and are rather ineffective in the case of products which are already relatively strongly coloured.
German Auslegeschrift 1,238,918 describes a process of stabilisation of epoxide compounds against discolourations, for example through heat exposure, by addition of 0.05 to 3.0% of organic peroxides. However, this process applies to measures during subsequent use of the epoxide compounds.
Swiss Patent Specification No. 442,262 describes a process for the manufacture of solid polyglycidyl ethers which on average possess more than one epoxy group per molecule and have a Durrans softening point of at least 50.degree.C, the process being carried out in the presence of sodium dithionite and/or under a nitrogen atmosphere. This procedure, which inherently is only intended for use in the manufacture of higher-molecular polylycidyl ethers, however only gives products of Hazen colour indices of 100-150 and such values are even attainable without the recommended measures if the starting substances are of perfect quality.
The patent literature describes several processes for the manufacture of glycidyl ethers which use catalysts for the chlorohydrin ether formation. The processes are in some cases very involved and the products of the process also do not have the desired low chlorine contents.
According to the process described in USA Patent Specification No. 3,336,342, polyhydric phenols are reacted with epihalogenohydrins in the presence of sulphonium salts, or compounds containing sulphur which can react with epihalogenohydrin to give sulphonium salts, to form the corresponding halogenohydrins from which, after removing the excess epihalogenohydrin, hydrogen halide is split off so as to arrive at the desired epoxide compounds. This process is very time-consuming, since the formation of the chlorohydrin ether requires at least 40 hours. Furthermore, the excess epihalogenohydrin distilled off contains some dihalogenohydrin and must be worked up separately before being reused. For these reasons the process is very time-consuming, involved and uneconomical.
According to the process described in USA Patent Specification No. 3,372,142, not only carboxylic acids but also phenols are converted into the chlorohydrin compounds by means of excess epichlorohydrin in the presence of benzyltrimethylammonium chloride or anionic exchanger resins and thereafter converted into the epoxide comounds with an aqueous solution of an alkali metal hydroxide which is saturated with an alkali metal carbonate. Here again it is found that the process is muct too time-consuming for practical use since the formation of the chlorohydrin ether required 25 hours. Including the working up of the chlorohydrin ether to give the epoxide compound, which would require a further 10-15 hours, the kettle dwell time would be unacceptable in practice.
A similar process is described in USA Patent Specification No. 2,943,096, accordingn to which, again, polyhydric phenols and epichlorohydrin are converted into the chlorohydrin ether, in the presence of tetramethylammonium chloride or benzyltrimethylammonium chloride. This again requires 25 hours. The further working up of the reaction batch proves to be very expensive since the excess epichlorohydrin, after being separated off by distillation, must be worked up with sodium hydroxide solution because of its dichlorohydrin content, to give a purer epichlorohydrin which can be reused. The chlorohydrin ether isolated is dissolved in a solvent mixture of toluene/ethanol and converted into the glycidyl ether by reaction with 18% strength by weight aqueous sodium hydroxide solution. Here again the individual process steps require a great deal of time so that this process cannot be regarded as very economical.
According to the data in Netherlands Published Specification 69/08790 excess epichlorohydrin is reacted, in a first stage, with a polyphenol in the presence of a catalyst, for example a quaternary ammonium salt to give the chlorohydrin ether, the conversion being at least 80% and preferably at least 90%, relative to the phenolic OH groups. In the second stage, an aqueous sodium hydroxide solution which contains 0.80 to 0.99 equivalent of sodium hydroxide per phenolic OH group is added, water being distilled off azeotropically. The glycidyl ether is additionally subjected to a post-dehalogenation.
According to the disclosures in Netherlands Published Specification 70/08287 excess epichlorohydrin is reacted, in a first stage, with a polyphenol in the presence of a catalyst, for example a quaternary ammonium salt, to the chlorohydrin ether, the conversion being at least 5%, but less than 80%, relative to the phenolic OH groups. In the second stage, an aqueous sodium hydroxide solution which contains 0.80 to 0.99 , preferably 0.92 to 0.98, equivalent of sodium hydroxide per phenolic OH group is added, water being distilled off azeotropically whilst recycling the dehydrated epichlorohydrin. The glycidyl ether is additionally subjected to a post-dehalogenation. The quoted contents of easily saponifiable chlorine in the resulting products of the process are between 0.75 and 0.20% by weight.
It is the task of the present invention to provide a process for the manufacture of glycidyl ethers of monohydric or polyhydric phenols having low contents of hydrolysable chlorine, which gives excellent results even on an industrial scale and can be carried out in an economically advantageous manner.